1. Field of the Invention
The present invention relates to a high temperature equipment which is usable in a high temperature corrosion environment due to corrosive components as well as in an erosion environment due to flying particles.
2. Description of the Prior Art
Taking example of a gas turbine, it is a recent tendency that a low quality fuel is going to be used for cost reduction of gas turbine operation. Of the low quality fuel, in a turbine operated by fuel obtained by coal gasification at a pressurized fluidized bed boiler, as compared with natural gas fuel or oil fuel as so far been used, there are produced a severe high temperature corrosion environment due to corrosive components of Na, K, Cl, S, etc. as well as an extremely severe erosion environment due to flying particles.
Thus, in order to enhance the corrosion resistance in a high temperature portion of the gas turbine using fuel obtained by coal gasification at the pressurized fluidized bed boiler, especially in a turbine moving/stationary blade used in a severe operation condition, there is employed an element having an aluminum diffusion layer formed thereon by an aluminum diffusion coating, as shown in FIG. 4(a), or an element having a spray coating of MCrAlY (M: Co, Ni, Co+Ni, Fe) formed thereon, as shown in FIG. 4(b). But, essentially with respect to these coatings, main object thereof is a corrosion resistance and reduction of erosion due to flying particles is a secondary one.
Also, as shown in FIG. 4(c), there is often used a spray coating of chromium carbide [75 wt % Cr3C2xe2x88x9225 wt % (50 wt % Nixe2x88x9250 wt % Cr)] as an erosion resistant coating for steam generator tube and the like which are under an erosion environment.
However, while this spray coating of chromium carbide is excellent in the erosion resistance by virtue of the finely dispersed Cr3C2, quantity of matrix (binding material) contained therein is small and from view point of its ductility and toughness, it is not used for turbine blade which is a rotational element.
Another reason for being not used for the turbine blade is that Nixe2x80x94Cr alloy of the matrix is inferior to the MCrAlY coating in the corrosion resistance and oxidation resistance in a high temperature. Thus, in the prior art gas turbine moving/stationary blade used in such a severe environment, there arises a problem that life of the turbine blade is shortened extremely. It is to be noted that the temperature of damageable portion in such a case is approximately 600 to 800xc2x0 C.
In view of the problem in the prior art, therefore, it is an object of the present invention to provide a high temperature equipment, such as a gas turbine high temperature portion, which is usable in a high temperature corrosion environment due to corrosive components as well as in an erosion environment due to flying particles.
In order to attain said object, the present invention provides a high temperature equipment whose base material 1 has a coating layer formed thereon in which Cr3C2 which is excellent in a high temperature erosion resistance is finely dispersed in a matrix MCrAlY which is excellent in a corrosion resistance and oxidation resistance, as shown in a schematic cross sectional view of FIG. 1, so that life of a high temperature portion of turbine blade, steam generator tube and the like may be elongated.
The MCrAlY is a generally used one for the corrosion resistant and oxidation resistant coating and representative ones thereof are shown in Table 1 together with chemical compositions.
Mixing ratio of MCrAlY to Cr3C2 is (50xcx9c75):(50xcx9c25) in weight ratio, that is, MCrAlY/Cr3C2=1/1xcx9c3/1. This is for the reason that if ratio of Cr3C2 is less than 25%, effect of the erosion resistance becomes low and if ratio of Cr3C2 is beyond 50%, toughness of the coating, when used for a rotational element, becomes low to crack easily.
In working the coating layer of the present invention, like in the case of conventional MCrAlY, there can be used various spraying methods, such as a low pressure plasma spraying (LPPS), an atmospheric pressure plasma spraying (APS), a high speed flame spraying (HVOF) and the like. Spray powder is made such that MCrAlY powder is mixed with Cr3C2 powder sufficiently at a ball mill and then is classified to each particle size distribution which is appropriate for the kind of spraying work.
The powder particle size distribution is classified according to the particle size distribution generally specified by the respective spraying apparatus manufactures. That is, the particle size distribution of 45 xcexcm or less is used for LPPS, that of 45 to 106 xcexcm is used for APS and that of 16 53 xcexcm is used for HVOF.